1. Field of the Invention
The invention relates to a modular drill with indexable cutting inserts having diamond cutting edges.
2. Background of the Invention
A modular drill is a drill consisting of interchangeable and disposable tips mechanically attached to a drill body. FIG. 1 illustrates such a modular drill 10 having a shank 15 extending along a longitudinal axis 20. The front end 25 of the drill 10 is moved axially along the longitudinal axis 20 such that a central pilot drill 30 and outboard inserts 35, 40 engage a workpiece and produce a hole extending therethrough. Typically, such modular drills have utilized a central pilot drill 30 comprised of cemented carbide and the outboard inserts 35, 40 also comprised of cemented carbide, which may or may not have coatings thereupon. However, while this configuration may be suitable for some materials, the applicants have found that such a configuration is undesirable when machining materials such as fiberglass. In particular, fiberglass material tends to build up on the cutting edges of the cemented carbide inserts and, as a result, their effectiveness for machining fiberglass is greatly reduced by this and additionally by abrasive wear. For different reasons, these same inserts are not suitable for machining titanium. In particular, titanium is known for its toughness and typical cemented carbide inserts do not have the properties necessary for machining this material. As illustrated in FIG. 1, outboard inserts 35, 40 are secured within a pocket 45, 50 by hold-down screws 55, 60 and, generally speaking, with attention directed to insert 40, include three cutting edges 65, 70, 75. Each cutting edge 65, 70, 75 for this particular cutting insert 40, includes, for example, a first cutting edge segment 65a and a second cutting edge segment 65b. The general configuration of insert 40 is known in the industry as a trigon shaped insert. For simplicity, outboard inserts 40 will be discussed with the understanding that the same discussion applies to the outboard insert 35.
The central pilot drill 30 protrudes from the front end 25 of the drill 10 and is the first portion of the drill 10 to contact the workpiece. In the past, the outboard inserts 35, 40 were comprised entirely of a cemented carbide substrate with coatings thereupon while the central pilot drill 30 has been comprised of a similar material. However, this design is not well suited for machining fiberglass because of abrasive wear and because the cutting edges of the carbide inserts encounter a build-up of fiberglass material, thereby, not only dulling the cutting edge, but furthermore, degrading the quality of machining capable by the modular drill 10.
As illustrated in FIG. 1 and with respect to cutting insert 40, the hold-down screw 60 may be removed such that the outboard insert 40 may be indexed within the pocket 45 to present a new cutting edge, whether it be cutting edge 70 or 75 to the workpiece. Once properly indexed within the pocket 50, the hold-down screw 60 may again be tightened to secure the outboard insert 40 within the pocket 50.
A design is needed to enhance the capability of the modular drill 10 so that it is capable of effectively machining fiberglass and/or titanium.
Additionally, it may be difficult to determine whether a cutting edge 65, 70, 75 has already been used for a machining operation. Depending upon the insert wear, the insert either should not be used again or should be used for a limited time. In the past, typically, the surface of inserts has been marked with inkjet print to identify cutting edges and to permit them to be indexed in a sequence. However, the inkjet printed labels frequently cannot withstand the harsh operating conditions experienced by the cutting insert and, under these circumstances. The inkjet printed label wears off such that it is no longer visible. Therefore, a design is needed to label the top surface of the cutting inserts 35, 40 such that not only can each label withstand the harsh conditions during a machining operation, but furthermore, each label will retain its visibility such that, after a machining operation, the cutting insert may be easily indexed based upon the pre-existing indicia on the face of the insert.